In Hyperion, the AI's pose two realities about the future interstellar war, either an internal war within AI with the Shrike being used as weapons or a war between surviving humans and the Core. And the Time Tombs are the future creation of the Core's Volatile's in the first scenario or human's for the second? Is this correct?
As said by Ummon to Brawne and the first Keats persona:
The time tombs are artifacts sent back to carry the Shrike/Avatar/Lord of Pain/Angel of Retribution/half-perceived perceptions of an all-too-real extension of our UI.
On the other hand, the tombs are described to begin their voyage back in time RIGHT AFTER the battle between Kassad and the humans against the Shrike army in the distant future , obviously without containing any Shrike/s within it.
So, I guess you are correct - those are the 2 possible futures, and Kassad defeating the Shrike in the future meant that the 1st option was replaced by the 2nd during the events described in The Fall of Hyperion.